It has been hitherto disclosed as an invention on an aluminum composite, for example, the Japanese Unexamined Patent Publication No. 05-05179, which discloses such a process for producing an aluminum composite that a particulate of polytetrafluoroethylene is electrochemically or chemically adsorbed on a surface of an anode-oxidized coated film of aluminum or an aluminum alloy, and after dried, it is lapped with an opposite material, so that an aluminum composite which is excellent in friction and wear property and baking resistance is produced. This disclosed reference is, in other words, the publication disclosing the invention of a surface treating method for treating the surface of aluminum in which the lubricant film is formed on the surface of the anodic oxidation coating of the aluminum.
Further, there is disclosed in the Japanese Unexamined Patent Publication No. 2001-172795, the inventions on an aluminum composite reduced in discharging gas and particles and improved in insulation and corrosion resistance and on a method for surface-treating the aluminum composite, in which a polysilazane solution is applied on the surface of the aluminum composite with an acidic oxide film formed on a substrate formed from aluminum or aluminum alloy, dried and baked to surface-treat the composite.
Thus, those inventions disclosed in these cited references are directed to a method for surface-treating the aluminum material, and are not directed to such a composite of aluminum material formed from aluminum or aluminum alloy raw material by applying it to an anodic oxidization treatment, and an synthetic resin molding that is strongly bonded together, and a process for producing the composite, which are the purpose of the present invention as will be described below in detail.
In the meantime, the conventional production of a composite of aluminum material and a synthetic resin molding is not only troublesome, but also there is not obtained a safe and fast composite which is large in a mechanical strength and of which the overall surfaces of the two constructional members thereof are bonded together.
Further, it has been hitherto carried out that using a conventional metal mold for insert molding, a composite is produced in such a manner that a portion of a metallic component made of iron or steel is inserted into the cavity of the metal mold, and while being held under this inserted condition, molten synthetic resin is injected into the cavity, so that a composite in which the portion of the metal component is inserted in a synthetic metal molding in a predetermined shape is produced.
However, in the case where the metallic component is made of aluminum raw material, because the surface thereof is the metallic one of aluminum or an aluminum alloy, and because coefficient of linear expansion of the synthetic resin to be molded by the insert molding and that of the aluminum are much different, it is difficult to produce a composite thereof.
Now, as generally known, production of assembled products of various electric and electronic parts of personal computers, digital cameras, pocket telephones, fittings for chassis or the like, electric and electronic containers such as casings or covers containing electric apparatus or electronic apparatus, and various kinds of parts for buildings, various kinds of parts such as ornamental parts for fitting to the inside or outside of motorcars, is performed by assembling an aluminum work prepared by previously press working a sheet of aluminum into a desired shape such as a predetermined case or cover, and a synthetic resin molding together by various assembly means to produce a composite. More in detail, some examples of the conventional composites are produced as follows. For instance, it is produced by stacking a press-worked aluminum plate and a synthetic resin mold each other through a pressure sensitive adhesive double coated tape. Alternatively, it is produced in such a process that a worked aluminum plate having a large number of caulking claws arranged on both side edges of the aluminum plate is manufactured, and a synthetic resin mold is placed on the aluminum plate, and in this state, the large number of the claws are inwardly bent on the surface of the synthetic resin mold. Further, alternatively, in stead of assembling them together by caulking of the large number of the claws, it is produced by fastening the mutually stacked members together using screws.
A composite as shown in FIG. 20 is a cover for a switch box showing one example of the former. This composite is produced as follows. Namely, after the container of a worked aluminum A shaped by press working a sheet of aluminum into the cover having at its center a hole for passing distributing electric wires, and a synthetic resin molding B formed by an injection molding process are prepared separately, the rear surface of the aluminum cover A and the flat surface of the synthetic resin mold B are overlapped with each other through a pressure sensitive adhesive double coated tape C and adhered together by pressing, so that a composite thereof is produced.
In addition, in the case of fitting synthetic resin made studs, which is used for mounting a chassis for an electric apparatus, and to the inner surface of the aluminum cover or case, so as to produce a composite of the two component, it is a conventional method that the two components are adhered together through an adhesive.
Thus, the conventional processes for production of composites each composed of an aluminum material and a synthetic resin mold requires such steps that the formed aluminum plate by press working and the synthetic resin mold are respectively made previously, and the two components are then assembled together by the above mentioned various joining means, so that it takes much time and troublesome in production thereof, resulting in lowering the production efficiency and increasing the manufacturing costs. Further, among the composites produced, the ones produced using the pressure sensitive adhesive double coated tape or an adhesive agent, there is brought about deterioration of the quality of the adhesive agent with the lapse of time and weakening the strength thereof. And, the ones assembled by caulking or screwing them together are not bonded together extensively or completely between the mutually opposite surfaces thereof, so that there is brought about such problems that the mechanical strength of the composites is weak as a whole, and is unreliable against vibrations and impact, so that a stable and fast composites can not be obtained.
Further, in the case of producing the composite produced by a so-called casting using a metal mold for injection-molding, in which a portion of the aluminum material is inserted into the cavity of the metal mold, so that there is brought about such inconveniences that a tensile strength of the joint portion between the synthetic resin molding and the inserted portion of the aluminum material is weak and is peeled from reach other by vibrations and impact to become shaky.
Accordingly, in view of the above-mentioned conventional problems, the purpose of the present invention is to produce at high efficiency and economically a stable and fast composite which, without requirement of the pressure sensitive adhesive doubled coated tape, adhesives, binding members such as a screw and a step of assembling of the two members, the mutually opposite surfaces of an aluminum material of any desired shape and size made of aluminum or aluminum alloy and a synthetic resin mold of any desired shape and size are bonded together strongly over the whole surfaces thereof to become large in peel resistance.
To achieve this purpose, various tests, researches and trial and errors have been carried out, and as a result, the inventors have found that when an aluminum raw material is subjected to an anodic oxidization treatment so that an aluminum material provided with an anodic oxidation coating having a predetermined diameter of pores may be formed, thereby a synthetic resin material is very strongly coupled with the anodic oxidation coating of the aluminum material, so that a composite which is very large in peel resistance can be obtained.
More in detail, it has been found out, in the course of tests and studies, that in the test case where the surface of the aluminum raw material was subjected to an anodic oxidization treatment to be formed with the anodic oxidation coating in a sulfuric acid bath with an alternating current electrolysis or a direct current electrolysis, there was obtained the anodic oxidization coating provided with an innumerable number of surface opening pores of which the diameter of the majority of the surface open pores was about 10 nm. When the aluminum material having the anodic oxidation coating was then placed in a recess made in one of metal molds for injection molding, and the other metal mold provided with a cavity formed in a predetermined shape was closed, and molten synthetic resin was injected into the cavity to be filled therein under pressure, and after cooling, the closed metal molds were opened, and a resultant composite product was taken out.
When a tensile strength was applied to the synthetic resin mold of the composite, the synthetic resin molding was peeled off easily from the anodic oxidation coating of the aluminum raw material due to a small tensile strength. When the anodic oxidation coating was observed in order to study the cause thereof, it has been found that the surface open pores thereof are too small that the molten synthetic resin can not be invaded into the pores. Now, instead of the sulfuric acid bath, using an oxalic acid bath, a phosphoric acid bath, a sodium hydroxide bath etc, electrolysis by a direct current was carried out and there were obtained respective aluminum materials having respective anodic oxidation coatings, and for the respective aluminum raw materials, they were subjected to the foregoing injection molding using the foregoing metal mold for injection molding, so that respective composites in which the synthetic resin moldings were coupled with the respective anodic oxidation coatings of the respective aluminum raw materials. When the tensile strength was applied to teach of the respective synthetic resin moldings thereof, the composite using the oxalic acid bath was peeled easily. However, the composite using the phosphoric acid bath and the sodium hydroxide bath, the synthetic resin molds of the respective composites were not peeled off even by a very large tensile strength. Now, after the synthetic resin molds of the respective composites were cut off from the respective anodic oxidation coatings thereof, it was observed that the innumerable pores of the respective anodic oxidation coatings were filled with solidified synthetic resin. Thus, as a result of the comparative tests, it has been found out that if molten resin is invaded into at least most of the innumerable pores, not to mention all of the pores, in the time of the molding process, molten resin is invaded into these pores, and as a result of the solidification, a composite is produced in which the synthetic resin molding is coupled strongly with the aluminum raw material in such a condition that synthetic resin molding is intruded into the pores.